Debugger: Fix display in separate Window

TreeModel::forAllChildren and TreeModel::walkTree differ
in the handling of the topmost item.

Change-Id: Id2032f69bb47218292507d33ed00935874afa73f
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/debugger/watchhandler.cpp

@@ -1301,6 +1301,7 @@ bool WatchHandler::insertItem(WatchItem *item)
 
     item->update();
 
+    m_model->showEditValue(item);
     item->forAllChildren([this](WatchItem *sub) { m_model->showEditValue(sub); });
 
     return !found;